The home office last night demanded an explanation from the Spanish government into how General Augusto Pinochet's confidential medical report was leaked to newspapers in Spain and Chile.

The report concludes that the former Chilean dictator suffers from brain damage brought on by multiple strokes and is unfit to stand trial on charges of human rights abuses. It was released to two Spanish newspapers by the foreign ministry of Spain within hours of it being delivered.

A newspaper in the Chilean capital of Santiago reported that it had been given extracts by the Chilean government. Chile was not an official recipient of the report, prompting sources close to the case to suggest that "supposed friends of the general's may be playing games".

The panel of British doctors who examined the former dictator in London last month said in part: "It is our view that Senator Pinochet would not at the present be mentally capable of meaningful participation in a trial. We base this opinion on:  Memory deficit for both recent and remote events Limited ability to understand complex sentences and questions owing to memory impairment, and consequent inability to process verbal information appropriately Impaired ability to express himself audibly, succinctly and relevantly  Easy fatiguability."

His condition has appreciably worsened during his time in Britain, and he has suffered a number of falls in the garden of the house on the Wentworth estate in Surrey where he has been under house arrest since being detained in London 16 months ago for possible extradition after a Spanish court issued a warrant alleging human rights violations during his 1973-90 rule in Chile.

While the general is homesick and bored, the doctors' report says he is not currently depressed and that his sense of humour "remains intact".

In a statement the home office said it had asked the Spanish authorities, through the crown prosecution service, their legal representatives, for information regarding how the conclusions of the report came to be disclosed.

The general's lawyers have written to the home secretary and the attorney general requesting an investigation into the leak, a potential contempt of court.

Earlier this week the high court ruled that the four states with outstanding extradition warrants against the general, Spain, Belgium, France and Switzerland, were entitled to see the report, which carries the conclusions of the three doctors who examined the general last month.

The report, ordered by home secretary Jack Straw to determine whether the general was fit to be extradited to Spain, was sent to Madrid in strict confidence and then passed to the investigating magistrate who first ordered the general's arrest, Baltasar Garzon.

The judge sent a letter yesterday to the national court in Madrid denying that had anything to do with a leak.

"It was a case of the foreign ministry leaking it before Garzon had a chance to do so," said one source.

Many of the documents in the Pinochet case have found their way into Spanish newspapers. An official at Belgium's foreign ministry, which initiated the hearing that led to the release of the medical papers, said last night his ministry "regretted" the breach of confidentiality.

He said a doctor appointed by a Belgian judge to examine the medical findings would report to the foreign ministry within days. The four countries have until Tuesday to pass comments to Mr Straw.

Human rights groups appeared split. "If the conclusions are correct then Gen Pinochet should not stand trial and should be returned to Chile," said Reid Brody of Human Rights Watch.

But other doctors might produce different conclusions: "We would hope that the states study the actual results of the tests and determine whether the proper legal standards have been applied."

Amnesty International demanded that a final decision on the general's fitness to stand trial be made in court.